This invention relates to the preparation of porous ceramic bodies by the pyrolysis of curable organopolysiloxanes filled with silicon carbide powders and, optionally, organopolysiloxane curing agents and sintering aids. This process is advantageous in that both the green bodies and the resultant ceramics have high strengths.
Various methods for the production of porous silicon carbide ceramic bodies are known in the art. For instance, it is known to mold mixtures of large particle size silicon carbide and smaller size silicon carbide into a desired shape followed by pyrolyzing the molded mixture to form a ceramic. The particle size variation in this approach creates the desired pores. Similarly, it is known to mold a mixture comprising a carbonaceous binder, silicon carbide powder and a silaceous powder into the desired shape followed by pyrolysis. In this approach, the carbon formed by pyrolysis of the carbonaceous binder reacts with the silaceous binder to form silicon carbide, thus, leaving pores in the sinter. Neither of these approaches, however, encompasses the use of organopolysiloxanes as binders to form porous ceramics.
Suganuma et al. in the Journal of Materials Science, 28 (1993) pp. 1175-1181, teach the formation of porous silicon carbide bodies by pyrolyzing a mixture of SiC powder, polysilastyrene and an organic binder. The reference, therefore, differs from the present invention in that it requires the use of an organic binder and it does not mention the use of polyorganosiloxanes.
Atwell et al. in U.S. Pat. No. 4,888,376 teach that high density silicon carbide bodies (&gt;2.4 g/cm.sup.3) can be formed by molding a mixture comprising an organopolysiloxane, a sintering aid, an organopolysiloxane curing agent and silicon carbide powder and then heating the molded mixture to a temperature above about 1900.degree. C. This reference, however, teaches that the bodies are highly densified compared to the high strength porous bodies described herein.
The present invention provides porous ceramic products using organopolysiloxanes as binders. Both the green bodies and the resultant ceramics have high strengths.